1. Field of the Invention
This invention relates to a rolling bearing apparatus, such as a bearing apparatus for the swing arm of a magnetic disk drive or hard disk drive (HDD), that is suitable to be used in locations where there is high-speed small rocking motion.
2. Description of the Related Art
In the case of the prior art bearing apparatus for a swing arm as shown in FIG. 5 where the left side is the VCM side, the pivot unit comprises a pair of grease-sealed ball bearings 100, a shaft 200 and a housing 300, and pre-loading is applied to the ball bearings 100.
In the case of this prior art bearing apparatus, the pair of ball bearings 100 have an inner race 101 and outer race 102, respectively, and adhesive is applied to four locations on the inner-diameter surface of the inner races 101 and the outer-diameter surface of the outer races 102 in the pair of ball bearings 100, to form the pivot unit, where the inner races 101 and outer races 102 are fastened to the shaft 200 and the housing 300, respectively.
Also, adhesive is applied to the outer-diameter surface 301 of the housing 300 of the pivot unit, which is constructed as mentioned above, and the pivot unit is fastened to the swing arm 400 in which a voice coil motor (VCM) is installed (on the left side in the figure). The pivot unit can be fastened with a bolt instead of adhesive.
Also, in order to apply the pre-load to the rall bearings 100, a method of controlling the load (loading by dead weight or spring force) or a method of controlling the axial rigidity (resonance) have been proposed (for example Japanese Patent Publication No. Toku Kai Hei 6-221326, U.S. Pat. No. 5,509,198).
Recently, there is an increasing demand for higher-density magnetic disk drives. In order to accomplish this, the track width of the tracks for recording signals on the disk have become increasingly more narrow, and therefore there is a demand to increase the speed for accessing a target track by the swing arm in which the head for recording and reproducing the signals is installed, as well as increase the positioning precision of the swing arm. Moreover, as the track width becomes narrower, it is desired that the amount that the magnetic head floats above the disk be decreased.
In order to do this, the height of the reference surface where the pivot unit is installed on the base (partly shown on the right side in FIGS. 6 to 10), and the height of the reference surface where the swing arm is installed must be precisely controlled.
Furthermore, as devices become more compact and thinner, particularly in the case of the HDD used in a notebook PC or mobile terminal that is 2.5 inches or less, there is a big demand to make the pivot unit more compact. In other words, in order to satisfy the demand for faster and more precise control as well as a more compact device, for the ball bearings that support the swing arm 400, it is desired that the assembly height T between the reference surface Q of the flange 201 (surface abutting to the base 700) in the shaft 200, and the reference surface P for swing arm installation (see FIGS. 6 to 10) be controlled and made more compact.
In the figures, B is the distance from the reference surface P for swing arm installation of the housing 300 to the abutting surface 100b of the outer race 100a of the bearing 100 on the side of flange 201, H is the thickness of the flange 201, H2 is the height of the bearing 100, Ti is the difference in between the outer and inner races with reference to the front surface facing the base (in FIGS. 7 and 9) and D is the width of the spacer (in FIG. 8).
In FIGS. 6 to 10, the retainer, which keeps the balls of the bearing 100 evenly spaced, and the seal, which prevents lubrication from scattering, and the swing arm 400 are not shown.
In the figures, a fastening screw 600 is threaded into the shaft 200.
FIG. 6 shows an example of using a housing 300 having an stepped inner diameter portion 302, and FIG. 7 and FIG. 8 show an example of using a spacer 500 between the pair of ball bearings 100 with no housing used. FIG. 5 is an example of outer races 100a having differing outer diameters.
The prior art bearing apparatus for a swing arm shown in FIG. 6 to FIG. 10 is constructed such that the inner race 101 of the ball bearing 100 on the side of flange 201 comes in contact with the flange surface 202 of the flange 201, and the height T between the reference surface Q of the flange 201 (to be mounted to the base) and the reference surface P of the swing arm installation is controlled by processing the each of the parts with high precision, however the cost was high.
Moreover, the so-called outer-race contact type is proposed e.g. by U.S. Pat. No. 6,010,247 in order to make the rolling bearing apparatus more compact. For example, the stepped section 302 on the inner diameter side of the housing 300 and the spacer 500 is done away with, and the end surfaces of the pair of outer races 100a come in contact with each other, and one of the inner races 100c comes in contact with the flange surface 202 of the flange 201 that is formed on the shaft 200. FIG. 9 shows the case of no housing and no spacer, and FIG. 10 shows the case of outer races have differing outer diameters and no spacer.
However, in this method as well, all of the parts must be processed with high precision and thus the cost is high. In other words, in order to accomplish this method, the tolerances for the thickness H of the flange 201, the height H2 of the ball bearing (including the difference T1 with the front surface), the housing dimension B (distance from the reference surface P for swing arm installation of the housing 300 to the contact surface 100b of the outer race 100a of the ball bearing 100 on the flange side), and the spacer width D are all added together, so the bearing apparatus must be selectively assembled by (1) reducing the tolerance range of each part and (2) measuring the tolerance of each part.